Revert "Merge branch '370640-pre-15-migrations-part-4' into 'master'"

Purpose of revert

!99014 (merged) added a migration with a January 2022 timestamp, but the MR is from October. This caused #408304 (closed), where upgrade paths from 15.x are broken. The reversion is for !116021 (merged), which is a migration squash.

I'm also adding some rubocop rules to ignore new rules that were previously "grandfathered", and disabling yamllint for .rubocop.yml to accommodate the necessary change. This should be reverted shortly and without incident.

Checklist

• Create an issue to reinstate the merge request and assign it to the author of the reverted merge request.
• If the revert is to resolve a broken 'master' incident, please read through the Responsibilities of the Broken master resolution DRI.
• If the revert involves a database migration, please read through Deleting existing migrations.
• Add the appropriate labels before the MR is created. We can skip CI/CD jobs only if the labels are added before the CI/CD pipeline is created.

Milestone info

• I am reverting something in the current milestone. No changelog is needed, and I've added a ~"regression:*" label.
• I am reverting something in a different milestone. A changelog is needed, and I've removed the ~"regression:*" label.

Related issues and merge requests